In general, a combustion apparatus, which is applied in cooking appliances using liquefied natural gas (LNG) or liquefied petroleum gas (LPG) as a fuel, performs a heating operation as sparks are ignited by bringing a gas fuel in contact with air. The heating from the combustion apparatus results in food being cooked.
That is, the cooking appliance is made of a metal, and includes a cooking body composed of one or plural grills on which a cooking vessel is placed, and a combustion apparatus formed in the grills.
In this case, the combustion apparatus is composed of a burner, a spark plug, and a thermocouple having a heating point of contact. The sparks are ignited from the spark plug and a heating operation is then performed with gas combustion in the burner only when the heating point of contact of the thermocouple is increased to a predetermined temperature or higher. When the heating point of contact of the thermocouple is not increased to the predetermined temperature, the sparks are ignited from the spark plug, but the heating operation is not performed with gas combustion in the burner.
Meanwhile, a gas fuel supplied to the combustion apparatus of the cooking appliance is usually supplied through a transfer pipeline from the outside to the inside of a building when the cooking appliance such as a gas range or a gas oven range is installed to be fixed.
That is, a gas fuel is guided and supplied from a gas supplier's storage tank through a transfer pipe buried underground, or guided through a gas supply pipe from a gas tank installed at the rooftop or outside the building. In general, one end of a middle valve (or a safety valve) configured to control the flow of a gas is connected to one end of the gas supply pipe, one end of a hosepipe is connected to the other end of the middle valve, and the other end of the hosepipe is connected to the cooking appliance.
Therefore, a gas is supplied from the gas supply pipe to a combustion apparatus installed at the cooking appliance through the hosepipe when the middle valve is open. As a result, when a user ignites sparks (for example, press the button or handles a rotary-type switch), a gas sprayed from the combustion apparatus burns to perform a heating operation.
Meanwhile, the combustion apparatus installed at the cooking appliances always has a risk of accidents since the gas is used as a fuel. In the prior art, various safety devices have been disclosed to solve the problems regarding the use of a gas fuel.
In one example, when a user forgets that food is being cooked using a cooking appliance, a vessel carrying the food is over-heated, resulting in the vessel being blackened and the food being burned, or even in a conflagration.
Therefore, the safety devices configured to sense overheating of a combustion apparatus when the combustion apparatus is overheated and automatically cut off the supply of a gas fuel have been disclosed in the prior art.
In this case, in the conventional gas safety devices, an electronic valve is configured to be electrically connected to a thermocouple so as to determine the supply of a gas.
That is, the gas safety device acts to sense sparks from a burner, convert the sparks into an electrical signal (i.e., a thermoelectromotive force), transfer the converted electrical signal to an electronic valve, and open the electronic valve to supply a gas to the burner. In this case, when the converted electrical signal is not transferred to the electronic valve, the gas safety device acts to close the electronic valve and cut off the gas supply to the burner.
However, the gas safety device does not precisely detect a heating state of the vessel since the gas safety device senses the sparks of the burner and converts the sparks into an electrical signal.
That is, the conventional gas safety devices serve to determine the opening/closing of an electronic valve using an electrical signal of the sparks rather than directly sensing a heating temperature of a vessel and determining the opening/closing of an electronic valve. In this case, a maximum running temperature of a thermocouple is approximately 600° C., and a boiling point of the contents in the vessel disposed at the burner is approximately 100° C. As a result, the moisture content in the vessel is evaporated, the vessel is overheated.
However, the conventional gas safety devices are run to sense sparks until a running temperature of a thermocouple reaches the maximum temperature of approximately 600° C., convert the sparks into an electrical signal (i.e., a thermoelectromotive force) and cut off the gas supply. Therefore, the conventional gas safety devices often malfunctions because the gas supply through the electronic valve is not cut off when the running temperature of the thermocouple does not reach a temperature of approximately 600° C. even though the moisture content in the vessel is completely evaporated at a temperature of approximately 100 to 150° C. and a surface of the vessel is blackened.